Heap Size Variations

[Y.S.Ramakrishna at Sun.COM]

-XX:+PrintHeapAtGC will show you the variation that Jon is talking about.

-- ramki

On 03/11/09 13:46, Jon Masamitsu wrote:
> I think you are seeing variations in the survivor spaces
> in the young gen.  If the two survivors are of different
> sizes (they are adjusted by GC ergonomics) you see something
> like this.  Actually the survivor spaces also grow and
> shrink so will cause changes).  Turn off the GC ergonomics
> (-XX:-UseAdaptiveSizePolicy). That will fix the sizes to
> the initial sizes.
> 
> On 03/11/09 12:37, Peng Du wrote:
>> Hello, guys
>>
>> I am doing some analysis on the parallel GC for the old generation. But 
>> I am confused by the output of -XX:+PrintGCDetails. I intentionally set 
>> the size of the heap to be [-Xms8m -Xmx8m]. However, the GC log 
>> indicated that the size of heap was varying in between every GC (minor 
>> and full). 
>>
>> For example:
>> ===============================================================================================
>> [GC [PSYoungGen: 768K->128K(896K)] 768K->320K(8064K), 0.0075060 secs] 
>> [Times: user=0.01 sys=0.01, real=0.01 secs]
>> [GC [PSYoungGen: 876K->128K(896K)] 1069K->406K(8064K), 0.0060870 secs] 
>> [Times: user=0.00 sys=0.00, real=0.00 secs]
>> [GC [PSYoungGen: 896K->128K(896K)] 1174K->507K(8064K), 0.0058220 secs] 
>> [Times: user=0.01 sys=0.00, real=0.01 secs]
>> [GC [PSYoungGen: 896K->128K(512K)] 1390K->699K(7680K), 0.0019780 secs] 
>> [Times: user=0.00 sys=0.00, real=0.00 secs]
>> [GC [PSYoungGen: 512K->64K(704K)] 1083K->727K(7872K), 0.0012320 secs] 
>> [Times: user=0.00 sys=0.00, real=0.00 secs]
>> [GC [PSYoungGen: 445K->154K(704K)] 1109K->838K(7872K), 0.0017830 secs] 
>> [Times: user=0.00 sys=0.00, real=0.01 secs]
>> [GC [PSYoungGen: 538K->144K(704K)] 1222K->848K(7872K), 0.0019050 secs] 
>> [Times: user=0.00 sys=0.00, real=0.00 secs]
>> [GC [PSYoungGen: 416K->32K(704K)] 1262K->882K(7872K), 0.0025930 secs] 
>> [Times: user=0.00 sys=0.00, real=0.00 secs]
>> [GC [PSYoungGen: 416K->32K(704K)] 1282K->906K(7872K), 0.0025650 secs] 
>> [Times: user=0.00 sys=0.00, real=0.01 secs]
>> [GC [PSYoungGen: 416K->176K(704K)] 1290K->1058K(7872K), 0.0022590 secs] 
>> [Times: user=0.00 sys=0.00, real=0.00 secs]
>> [GC [PSYoungGen: 560K->176K(704K)] 1442K->1098K(7872K), 0.0029060 secs] 
>> [Times: user=0.00 sys=0.00, real=0.00 secs]
>> [GC [PSYoungGen: 560K->64K(704K)] 1482K->1142K(7872K), 0.0014460 secs] 
>> [Times: user=0.00 sys=0.00, real=0.00 secs]
>> .......................
>> ===============================================================================================
>>
>> My analysis requires the heap size to be fixed as well as the relative 
>> ratio of each generation within the heap. Is there a way I can strictly 
>> restrict the sizes of the heap and each generation?
>>
>> Thanks!
>>
>>
>>
>> Peng Du
>>
>>
>> ------------------------------------------------------------------------
>>
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